QPID-4234: ensure configuration observers see queue deletion

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1373831 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/qpid/cpp/src/qpid/broker/QueueRegistry.cpp b/qpid/cpp/src/qpid/broker/QueueRegistry.cpp
index 5a30cd2..3521e08 100644
--- a/qpid/cpp/src/qpid/broker/QueueRegistry.cpp
+++ b/qpid/cpp/src/qpid/broker/QueueRegistry.cpp
@@ -77,7 +77,7 @@
         qpid::sys::RWlock::ScopedWlock locker(lock);
         QueueMap::iterator i = queues.find(name);
         if (i != queues.end()) {
-            Queue::shared_ptr q = i->second;
+            q = i->second;
             queues.erase(i);
         }
     }